Fluorescent Silica Hybrid Film-Forming Materials Based on Salicylaldazine

Abstract

Fluorescent film-forming materials were obtained by embedding salicylaldazine (SAA) in silica hybrids generated by sol–gel processes from different silane precursors in acid catalysis. Tuned local environments for the fluorophore were generated in the hosting network by modifying silica sols with organic groups through the co-condensation of tetraethylortosilicate (TEOS) and different alkoxysilanes hydrolysis products. The photophysical properties of the luminescent hybrid films were studied in direct relationship with structural, textural, and surface properties and based on interactions between SAA species and the silica hosting network. Film-forming materials were studied in order to determine differences in absorption and fluorescence emission due to the environments around the fluorophore. The variations recorded in the fluorescence emission spectra of the hybrid films were related to interactions established between the fluorophore species and their sterically hindered surroundings of the host hybrid silica, where free molecular motions are restricted. The influence of the type and amount of network modifier and of the fluorophore loading on the transparency of the films and fluorescence intensity was also investigated. The study carried out led to the elucidation of the necessary conditions for obtaining luminescent film-forming materials with high luminescence intensity and transparency useful for the design of new light concentrators.

Modeling the Properties of Curcumin Derivatives in Relation to the Architecture of the Siloxane Host Matrices

“…Pure curcumin derivatives in the polar environment of the silica matrix were characterized by the fluorescent emission peak at 545 nm for curcumin and 530 nm for the CA derivative [ 63 ]. The peak at 420 nm was given by the intermolecular interactions between the dye and the host matrix, as already presented by the authors in another paper [ 53 ]. The keto-enol and cis-trans tautomeric structures of the dyes were influenced by the size of the cages formed in the silica network, by the organic network modifiers PTES, DPDMES, and by the traces of polar solvents left in the cavities [ 4 ], following the sol–gel process.…”

“…Several different types of nanocomposites were obtained by modifying the mass ratio between the TEOS network generator and the PTES and DPDMES network modifiers ( Table 1 ). Nanosols were deposited as films which, as reported in the literature, [ 53 , 54 , 55 ] have different properties due to the intermolecular bonds established with the support and influenced by the hydrophobicity of the surfaces on which they are deposited ( Figure 2 ).…”

“…The siloxane polymer matrix was obtained by using the sol–gel process in acid catalysis [ 53 ]. By varying the silane precursors TEOS, PTES, DPDMES, and the mass ratio between them, four types of polymeric materials were obtained, in which curcumin derivatives were embedded ( Table 1 ).…”

“…They have the role of creating certain morphological structures in the network which can modify the general properties of nanocomposites and/or can create environments compatible with other organic or inorganic structures, that are to be incorporated in the siloxane matrix. Thus, organic–inorganic hybrid materials are obtained and deposited as thin films [ 51 , 52 , 53 ]. Depending on the field in which they are used, the nanocomposites must have certain properties and be compatible with the support on which they are deposited [ 54 , 55 ].…”